Please Help Diagnose Piston Failure

[Ramair08]

Hello Everyone,

I rebuilt this saw a couple years ago and it has been working great until this past weekend, I was cutting some wood and when I stopped to refuel it wouldn't start. I figured it must have vapor locked because it was so hot out so I let it sit for a while and it still wouldn't start. The next day I tried it again and still couldn't get it going so I pulled the muffler off and saw that a chunk of the piston was gone. Last night I pulled the cylinder off and this is what I found. It appears that it has been running for a while with piston broken. When I took it apart I could not find any pieces of the piston or ring.

I would have never thought it had anything wrong with it because it was running fine until I shut it off to refuel, there was no evidence that the spark plug had been hit by any shrapnel either.

When I rebuilt it I used an aftermarket piston and cylinder, Camber rings, new crank seals, I believe OEM circlips. When I got the new cylinder it was not finished the best so I smoothed the ports as best I could. I have only used 100LL gas at 40:1.

There is a new Golf piston on Ebay right now, would that be better than the other Chinese pistons available?

I am just wondering if anyone can shed some light on what happened.

 

[Mad Professor]

What sort of A/M P/C?

Looks like lots of stuff was dancing about the piston crown, before and/or after. What was the squish set at?

Any hardware missing from intake or exhaust?

 

[Chainsaw Jim]

It looks like it caught the exhaust port floor on the down stroke. The force of the exhaust would have carried the chunk out through the muffler. The piece is either lodged in your muffler or it cleared completely.
This is the reason why most don't use aftermarket cylinders. It is likely you didn't chamfer and shape the edges of the exhaust port properly to cause this.
I'll use a used oem cylinder before I'll ever use a brand new aftermarket one.

 

[Ramair08]

The cylinder was a "suitable replacement" that I found online. There isn't much for aftermarket parts available on these saws. The original cylinder was scored (but did clean up pretty good) and at the time I thought this would be a better way to go. It is very likely that I didn't have the edges properly shaped on the port. Should I try to get that Golf piston and new Camber rings and put it back into the old cylinder? I do have a complete 2095 parts saw (with scored piston) that I haven't taken apart yet to check the cylinder. Maybe I will try cleaning that one up too and run the better one.

 

[Ramair08]

What sort of A/M P/C?

Looks like lots of stuff was dancing about the piston crown, before and/or after. What was the squish set at?

Any hardware missing from intake or exhaust?

I didn't notice that any hardware was missing, I really can't recall what the squish was at. It had 165 PSI after it had a few tanks through it.

 

[Chainsaw Jim]

Can you get a really good macro pic of your oem cylinder? We might be able to tell you if it can pass or not.

 

[Ramair08]

Can you get a really good macro pic of your oem cylinder? We might be able to tell you if it can pass or not.

I will get that picture tonight, thanks for the help!

 

[belgian]

Looks like a fatigue failure to me....poor piston quality imo. Also the rings seem to be too thin (too much clearance in the gap), but the picture is not very clear. Did you use the rings that came with the piston ?

 

[fordf150]

Also the rings seem to be too thin (too much clearance in the gap), but the picture is not very clear. Did you use the rings that came with the piston ?

I see that too. not sure if our eyes are playing tricks on us or if those rings really do have that much clearance.

 

[Ramair08]

So I actually rebuilt this saw twice, the first time I used everything that came with the kit- piston, rings, bearing, cylinder, etc. Well it ran for about 10 minutes before the ring caught the exhaust and had a dramatic failure! So they sent me a replacement and I took the time to make sure the ports were not sharp (trying to copy how the original looked) and bought the correct Camber rings, I thought they fit tight in the groove but will check again tonight. I put it all back together and have used it for a couple years cutting alot of wood. It ran very strong and I couldn't tell anything was wrong until I took the muffler off.

 

[hotshot]

Did you use the rings that came with the piston ?

Roland, I think the OP used new Caber rings, but is calling them "Cambers"...regardless, that ring got broke, hung up on the port, or some other foreign object may have been in there.

Ramair08, did you check the ring end gaps with a feeler guage before you put it together?

 

[leeha]

Broken ring bouncin around in the ring groove. That ring
groove is some beat up.


Lee

 

[1Alpha1]

What is it with chainsaws and messed-up pistons?

I can't even begin to count the number of two-stroke dirt bikes I had, and I recall one time, I had a piston issue. Even then, it was a minor issue. I've yet to have any kind of a piston issue with a chainsaw, weed eater, or blower.

 

[Jacob J.]

Should I try to get that Golf piston and new Camber rings and put it back into the old cylinder?

The Meteor piston for Husqvarna 395 is a better choice. Use your old OEM cylinder if it's serviceable and go with a new Meteor 395XP piston kit with new OEM wrist pin clips. I've built a dozen 2094/2095s this way and it's worked well everytime.

 

[blsnelling]

Golf quality piston is your problem. Use either Meteor or OEM, nothing else.

Edit: I just now realize this was an aftermarket cylinder as well. Once of my biggest complaints is that the port shape is often flat or even convex. Stick with an OEM cylinder and an OEM or Meteor piston and you won't have these issues.

 

[drf255]

Looks like a casting flaw in the piston to me. It finally gave way.

When I've had a port chamfer issue, there was a groove in the piston and the rings where it had caught. I believe that it would have some damage between the first and second ring land if that had been the case.

 

[srcarr52]

Broken ring bouncin around in the ring groove. That ring
groove is some beat up.
Lee

It does look like the ring was broke before the piston got tore up. Maybe it was detonation or maybe the ring got pinched by not having enough squish clearance. The no carbon ring around the whole piston suggests that the squish was too tight and the really high squish velocity was keeping that area of the piston clean.

 

[Marshy]

Roland, I think the OP used new Caber rings, but is calling them "Cambers"...regardless, that ring got broke, hung up on the port, or some other foreign object may have been in there.

Ramair08, did you check the ring end gaps with a feeler guage before you put it together?

Bingo! Very important step right there. Also, making sure the proper ring is provided. However, I'm my experience with catching rings in ports, the ring usually gets folded back into the soft piston and goes for a ride up and down the cylinder wall. Maybe the ring was too thin for the ring land and beat the piss out of the piston. Where is the top ring did you take it off?

 

[blsnelling]

I suppose that's possible, but I have never seen a ring that was too tight.

 

[blsnelling]

That ring groove is some beat up.

I'm not sure that isn't lens distortion.